I have seen (and been involved in) plenty of these kind of incidents when diving on day boats in Australia and Egypt. The problem is that we are not talking about a dive club outing where people know each other and know each others limits, what they look like in the water and use a mutually understood sign language. Rather we are talking about a bunch of people who usually have only a few logged dives, are using hire gear, sometimes only have English as a second language (or not at all) and who don't know each other from Adam. These people will not normally talk to each other on the boat - often due to being nervous of seeming like a complete newbie. When it comes to jumping in the divemaster will often buddy people up at the last minute. This means that two dive buddies who don't know each other will shy away from buddy checks and enter the water with a quick nod being the extent of their buddyness.
Add to that a dozen people flapping around on the shot line, wearing wetsuits that you don't recognise (sometimes all exactly the same from the hire depot), the wrong weight in their belts and you get the idea that this is not going to be the most orderly outing...
Diving - it's so simple at normal rec levels. And yet I've seen it become v scary v quickly. DMs thinking that everyone should have plenty of air left and belting along in front - with divers at the back vainly holding their five fingers up to show.......who?
DMs taking divers up early and then the rest of the group going off in all directions.
So CHIARA - you did exactly the right thing, even though it messed up one of your dives. I'm sure you would have felt a lot worse if there had been an accident that you felt you could have helped to avoid.
MASS-diver - you are right, diving on tourist boats can be awful. However, for a lot of us it is the only option when on a 2 week holiday and I would think that it is under these conditions where the majority of diving is done for a lot of people.
All I'm trying to say is that whenever you dive in a group you should take some responsibilty for the safety of that group. Even though you are only a paying punter and the DM or dive leader should be responsible.
I've cut short a few dives due to buddies being unfamiliar with their brand new BCDs and regs etc and after what I've said to them afterwards I don't think they will ever be my buddy on the surface - but I'd sooner that than be sat in the police station explaining exactly what happened when they ran out of air......
Happy diving!
Mark